1. Field of Invention
The present invention relates generally to devices cooled by pulse tube coolers.
2. Description of Prior Art
Use of superconducting materials in electrical devices, including motors, generators, transformers, electromagnets, power transmission lines and a variety of electronic devices, has greatly improved their performance. However, all presently-known superconducting materials must be cooled to temperatures far below room temperature before they exhibit superconducting properties. For high temperature superconductors, cooling to about 50 Kelvin is desirable; for low temperature superconductors, cooling to less than 10 Kelvin is essential. Other electric, electronic, and electro-optical equipment performs better when cooled even though it is not fabricated using superconducting materials.
Various types of cryocoolers can provide cooling to temperatures required by superconducting devices. Those cryocoolers include Stirling, Gifford-McMahon, Vuilleumier, and pulse tube coolers. However, transfer of heat from superconducting devices to the heat-absorbing heat exchangers of available cryocoolers has proved to be a difficult and demanding task. Integration of cooling devices with rotating equipment has proved to be particularly challenging.
Several approaches to integration of cooling devices and rotating superconducting devices have been proposed. For example, U.S. Pat. No. 6,625,992 issued to Maguire, et al., teaches a bank of cryocoolers cooling a superconducting electric motor through a secondary pumped loop of helium cooled by those cryocoolers. U.S. Pat. No. 6,376,943 issued to Gamble, et al., teaches a closed circulation system, external to a cryocooler, for cooling a rotating superconducting device. U.S. Pat. No. 6,164,077 issued to Feger, recognizes the problem of transmitting heat from a cooling load to the external surface of the cold tip of a cryocooler even when the load is not rotating. U.S. Pat. No. 6,070,414 issued to Ross, et al., teaches a spring-loaded arrangement for interfacing the external surface of the cold tip of a cryocooler with its cooling load.
All of the previous approaches have depended upon drawing heat from the cooling load through the wall of the cooler and thence into the working fluid of the cooler. In all instances, the cooling load has been external to the envelope of the pressure vessel that contains the working fluid of the cooler.